The present invention relates to novel lubricating compositions and methods of preparing the compositions. The compositions comprise organo molybdenum compounds in an oil of lubricating viscosity. The compositions have improved high temperature frictional characteristics which translates into improved fuel economy when said compositions are used in an internal combustion engine.
It is known that organo molybdenum compounds can improve frictional characteristics of lubricating compositions. For instance PCT Patent Application WO 96/23856 by the Tonen Corporation discloses that molybdenum dithiocarbamate and molybdenum dithiophosphate improve the frictional characteristics of lubricating oil used in an internal combustion engine. The lubricating oil contributes to improved fuel economy by virtue of its reduced frictional properties.
PCT Patent Application WO 96/06904 by the same Japanese corporation discloses the use of an oxymolybdenum dithiocarbamate sulfide as an organo molybdenum friction reducer for use in lubricating oils for internal combustion engines. Both patent applications referenced above are incorporated herein by reference in their entirety and in particular for their disclosure of organo molybdenum compounds.
This invention comprises oils of lubricating viscosity compositions containing organo molybdenum compounds and methods of making said oils. The oils have reduced frictional characteristics which translates into improved fuel economy for internal combustion engines lubricated by said oils.
We have found that lubricating oil compositions which contain organo molybdenum compounds show improved frictional characteristics when said compositions are formed from separate semi-packages of additive components. In this we have found that improved friction characteristics result when the semi-package compositions comprise:
Semi-package 1: organo molybdenum compound and non-polar additives;
Semi-package 2: dispersant plus polar additives selected from the group consisting of metal-containing detergents, zinc salts, surfactants and mixtures thereof;
Semi-package 2 is mixed and heated for 0.25-6 hours at up to 110xc2x0 C. prior to use.
The semi-packages are then added to an oil of lubricating viscosity to form an oil composition having improved frictional characteristics.
It is known that friction modifiers which increase the lubricity of lubricating oils may operate by the absorption of polar components on the moving parts to be lubricated. Polar components may be metal-containing compositions such as detergents, zinc salts, and -surface active agents. Such absorption reduces the energy needed to move one part relative to another and thus reduce the coefficient of friction for the oil. We have discovered that the coefficient of friction of lubricating composition is effected by competition for absorption of polar components on said relatively moving parts.
Thus we have found that the tendency for absorption or various polar compounds relative to molybdenum dithiocarbamate is:
Zinc dialkydithiophosphate greater than molybdenum dithiocarbamate
Calcium sulfonate detergents greater than molybdenum dithiocarbamate
Surfactant greater than molybdenum dithiocarbamate
The conclusion above was reached by determining friction coefficients of oils of lubricating viscosity containing the additives listed. What the results mean is that in lubricant compositions containing organo molybdenum compounds together with zinc salts, metal-containing detergents and surfactants will not result in properties demonstrating the full lubricity improvement from the molybdenum compounds because of preferred absorption on moving surfaces of the non-molybdenum polar components.
We have found that the competitive effect of selective absorption by various components on surfaces to be lubricated can be reduced by the use of dispersants in the formation of selective separate additive semi-packages and the addition of said additive semi-packages to said oil.
Thus we have discovered that when the polar components shown above are first mixed and heated with a dispersant, then the tendency of absorption on surfaces to be lubricated is reversed from that shown above and molybdenum is at least about equally if not preferentially absorbed. This is illustrated as:
dispersant plus zinc dialkydithiophosphate less than molybdenum dithiocarbamate dispersant plus calcium sulfonate detergent less than molybdenum dithiocarbamate dispersant plus surfactant less than molybdenum dithiocarbamate
To demonstrate this invention, several individual components as well as mixtures of components were added to an oil of lubricating viscosity and friction coefficients were determined. As a starting point the friction coefficient of molybdenum dithiocarbamate was determined in a 100 neutral oil containing 1.2 weight percent of the molybdenum compound. The molybdenum dithiocarbamate is available as Adeka S-100 from Asahi Denka Kogyo K. K., Tokyo 103 Japan, and may also be purchased from the R. T. Vanderbilt company of Norwalk, Conn., U.S.A. FIG. 1 illustrates that the molybdenum compound reduces friction with time and temperature increase.
The organo molybdenum compounds which may be used in this invention are those listed above in WO 96/23856 and WO 96/06904 and those purchased from commercial sources such as R. T. Vanderbilt and Asahi Denka Kogyo K. K. listed above.
The Vanderbilt organo molybdenum compounds are MOLYVAN(copyright) A, a molybdenum oxysulfide dithiocarbamate; MOLYVAN(copyright) L, a sulfurized oxmolybdenum organophos-phorodithioate; MOLYVAN(copyright) 807, a molybdenum-sulfur compound; MOLYVAN(copyright) 822, an organo molybdenum dithiocarbamate; MOLYVAN(copyright) 855, an organo molybdenum complex and MOLYVANO 856 B, an organo molybdenum complex. Purchased organo molybdenum compounds are used as purchased. The organo molybdenum compounds also include those disclosed in U.S. Pat. No. 4,846,983 which is incorporated herein by reference for such disclosure. These are molybdenum carbamate compounds.